TEOM Tapered Element Oscillating

The tapered-element oscillating microbalance (TEOM) sensor, as described by Patashnick and Rupprecht, consists of an oscillating tapered tube with a filter at its free end (Fig. 13.40). The mass of the filter increases due to the collected aerosol and produces a shift in the oscillation frequency of the tapered tube that is directly related to mass. 

For the studies described in this chapter, a novel system was employed, namely the tapered element oscillation microbalance (TEOM), to monitor the dynamic process of carbon formation under real C02 reforming conditions. The use of TEOM enables carbon formation to be measured in situ, and kinetic studies of carbon formation to be performed at different partial pressures of CH4 and CO. 

Fig. 1. The tapered element oscillating microbalance reactor manufactured by Patashnick and Rupprecht (TEOM Series 1500 PMA Reaction Kinetics Analyzer). The term Cat. refers to the catalyst sample.

Tapered Element Oscillating Microbalance (TEOM) studies of catalyst reduction (Gladden and McGregor, unpublished results). These studies also yield an average 1 1 relationship between vanadium atoms and oxygen atom loss. 

The Tapered Element Oscillating Microbalance (TEOM) reactor has recently been applied to study deactivation of zeolite catalysts [7,8]. The main advantage of the TEOM reactor is that all gases in the reaction mixture are forced to flow through the catalyst bed as in a conventional fixed-bed reactor. Coupled with on-line gas chromatography, the catalyst activity, selectivity and coking rate can be measured simultaneously as a fimction of the amount of coke on the catalyst. Hence, the TEOM represents a unique way of studying the effect of coke deposition in detail. 

Kinetics and diffusion Steady-state isotopic transient kinetic analysis (SSITKA) Temporal analysis of products (TAP) Tapered element oscillating microbalance (TEOM) Temperature scanning reactor (TSR) Zero length chromatography (ZLC) Pulsed field gradient NMR... 

Measurements performed in a tapered element oscillating microbalance (TEOM) reveal that diffusivities can be derived from uptake data monitored under full reaction conditions. In this way the effect of acid leaching on the diffusional behaviour of w-hexane in Pt/H-Mordenite is investigated. It is shown that acid leaching largely enhances the -hexane uptake rate, but does not result in a net increase in the intracrystalline steady state diffusivity. It is concluded that the accelerated uptake after acid leaching merely arises from the shorter intracrystalline diffusion path resulting from the mesoporous structure. 

The experiments were performed in the Tapered Element Oscillating Microbalance (TEOM) reactor (7,8), in which carbon formation and deactivation could be measured simultaneously by coupling with on-line GC analysis. The dry reforming of methane was studied on an industrial Ni (11 wt%)/(Ca0)a-Al203 catalyst at temperatures of 500 °C and 650 °C, total pressures of 0.1 MPa and 0.5 MPa and a CO2/CH4 ratio of 1. The BET surface area of the catalyst was 5.5 m /g, and the Ni surface area 0.33 m /g. The detailed experimental procedures were similar to that reported previously (7). 

A convenient type of equipment for studies of this type is the tapered element oscillating microbalance (TEOM), developed by Patashnick and Rupprecht [1980] and shown in Fig. 5.3.3-2. The advantage of this equipment is that the full amount of gas is flowing through the element containing the catalyst bed, which is brought to oscillation. The evolution of the amount of... 

Figure 5.16. The Tapered Element Oscillating Microbalance (TEOM) can be used to monitor the amount of material being accumulated in the filter mounted on top of the glass element by measuring the change in the oscillation frequency of the element due to increasing mass, a) A system, incorporating a TEOM, which is used to monitor the respirable dust present in a working environment, b) Detail of the TEOM.

The equipment consists of a feed system, the reactor section, a GC, and an MS for product analysis. A Rupprecht and Patashnick TEOM 1500 PMA (Pulse Mass Analyzer) was used in the experimental design shown in Fig. 2. The tapered element with the catalyst bed on its end oscillates in a clamped-free mode. This is accomplished through a sensitive feedback amplifier control circuit connected to a mechanical drive to supply the necessary energy. The reactor tube is constructed of proprietary glass ( engineered glass ) (5). The reactor material has proved to be sufficiently inert for a number of applications. The catalyst bed is held in place by quartz, a-alumina, or carbon wool, depending on the conditions, and a metal cap. 

The TEOM technique was used to investigate adsorption, reaction, and coke deposition. The active element of TEOM consists of a tapered tube that maintains oscillation at its natural frequency. The natural frequency changes in terms of the mass change in the tapered tube. The mass uptake is then determined by the change of the oscillating frequency. The detailed... 

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